1. Field of the Invention
The invention relates to a nitric oxide reducing catalyst containing a negatively charged copper cluster and to a method for reducing nitric oxide and a method for producing nitrogen using the catalyst. The invention also relates to a catalyst containing a negatively charged copper cluster for reducing nitric oxide as well as oxidizing carbon monoxide and to a method for reducing nitric oxide as well as oxidizing carbon monoxide using the catalyst.
2. Description of Related Art
Noble metals have been conventionally used for catalysts with various applications. For example, noble metal catalysts such as platinum, palladium and rhodium have been used for cleaning up hazardous components contained in exhaust gas from automobiles and the like such as nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HC).
Methods for reducing NOx or oxidizing CO using various metals have been reported to date. For example, it has been reported that nitric oxide (NO) can be reduced to nitrogen (N2) with a rhodium cluster (The Journal of Physical Chemistry A 110, 10992-11000 (2006)), a bimetallic cluster containing gold and copper (Japanese Patent Application Publication No. 2012-217970 (JP 2012-217970 A)) or a cobalt cluster (Japanese Patent Application Publication No. 2009-90239 (JP 2009-90239 A)).
It has also been reported that carbon monoxide (CO) can be oxidized to carbon dioxide (CO2) with a negatively charged copper cluster (Japanese Patent Application Publication No. 2012-166175 (JP 2012-166175 A); and The bulletin of the Society of Nano Science and Technology 10(1), 41-44 (2011); and The European Physical Journal D67, 35 (2013)).
As described above, in spite of investigations on various metals in order to use them for reducing NO, noble metals have still been predominantly used. As noble metals are a precious resource, use thereof faces problems of increased cost. Oxidation of CO also faces the similar problem.